1. Field of the Invention
The present invention relates to a switch whose electrical connection state is switched by a linear reciprocating motion of a movable piece.
2. Description of Related Art
A switch used as a power window switch to be mounted in a vehicle or the like is provided with a movable contact and a fixed contact. The movable point is slid on the fixed contact in connection with a linear reciprocating motion of a movable piece and comes into contact with or separates from the fixed contact, so that it is kept to a close state or an open state (electrically conductive state or electrically non-conductive state).
FIG. 15 is a perspective view showing an example of a related art power window switch. A power window switch 51 serves to operate a power window at the side of the driver's seat of a vehicle, and it is provided to a switch module (not shown). A knob 52 is supported in U, D directions by inserting shafts (not shown) through holes 52a formed at both side surfaces of the knob 52. An operator 53 is provided inside the knob 52 so as to project downwardly. A slider 54 is fitted to the tip of the operator 53. A movable piece 55 is provided to the slider 54 by insert molding. The movable piece 55 is formed of metal having electrical conductivity, designed in an H-shape when viewed from the upper side, and has elasticity. The respective terminal portions of the movable piece 55 project from the right and left side surfaces of the slider 54 to the obliquely downward side. The tips of the respective terminals are provided with movable contacts 55a to 55d. The upper surface of the movable piece 55 is pressed by a wall (not shown) so that the respective movable contacts 55a to 55d of the movable piece 55 are brought into contact with the surface of the board 56 under predetermined pressure, and it moves in only the right-and-left direction in parallel to the board 56.
Fixed contacts 56a to 56e are provided onto the board 56 as shown in FIGS. 15 and 16. The fixed contacts 56a to 56e are formed of metal having electrical conductivity. An earth fixed contact 56e is grounded, and it is provided at the center so as to be wide. A manual-up fixed contact 56a, an automatic-up fixed contact 56b, a manual-down fixed contact 56c and an automatic-down fixed contact 56d are provided at the right and left sides of the earth fixed contact 56e in parallel to the moving direction of the slider 54 so as to be narrow in width. The manual fixed contacts 56a, 56c are provided so as to be nearer to the earth fixed contact 56e than the automatic fixed contacts 56b, 56d. In place of this construction, the five fixed contacts described above may be provided to the case of the switch cell in series in the right-and-left direction so as to be spaced from one another at predetermined intervals as disclosed in Japanese Patent No. 3,183,813 (Patent Document 1) described later. Furthermore, as disclosed in Japanese Patent No. 2,740,384 (Patent Document 2), three fixed contacts may be provided to wafer as the inner bottom surface of the case in series in the right-and-left direction so as to be spaced from one another at predetermined intervals.
When the knob 52 is located at a non-rotated neutral position as shown in FIG. 15, the movable contacts 55a to 55d of the movable piece 55 are separated from the respective fixed contacts 56a to 56e on the board 56, and the earth fixed contact 56e and each of the other fixed contact points 56a to 56d are kept under a non-conductive state. Under this state, a control circuit for a power window (not shown) does not rotate a motor as a driving source, and thus the power window does not move upwardly and downwardly. When the knob 52 is slightly rotated in the U direction, the movable piece 55 is moved to the left side through the operator 53 and the slider 54, the movable contacts 55c, 55d come into contact with the earth fixed contact 56e, and the movable contact 55a comes into contact with the manual-up fixed contact point 56a. Accordingly, the manual-up fixed contact 56a and the earth fixed contact 56e are conducted to each other through the movable piece 55, and the control circuit reversely rotates the motor during only the conduction period, whereby the power window is upwardly moved. Furthermore, when the knob 52 is greatly rotated in the U direction, the movable piece 55 further moves to the left, and the movable contact 55b also comes into contact with the automatic-up fixed contact 56b. Accordingly, the automatic-up fixed contact 56b, the manual-up fixed contact 56a and the earth fixed contact 56e are conducted to each other, and the control circuit reversely rotates the motor to move the power window upwardly until the power window is perfectly closed.
Conversely, when the knob 52 is rotated in the D direction, the movable piece 55 moves to the right side, the movable contacts 55a, 55b come into contact with the earth fixed contact 56e, and the movable contact 55c comes into contact with the manual-down fixed contact 56c. Thereafter, the contact state is continued, and the movable contact 55d comes into contact with the automatic-down fixed contact 56d. Accordingly, the manual-down fixed contact 56c and the earth fixed contact 56e are conducted to each other, the automatic-down fixed contact 56d also comes into contact with the earth fixed contact 56e, and the control circuit forwardly rotates the motor to move the power window downwardly during only the conduction period of the contacts 56c, 56e or until the power window is perfectly opened.
However, in the related art contact structure described above, the earth fixed contact 56e at the center and the manual fixed contacts 56a, 56c at the left and right sides are close to each other and the insulating interval between the contacts 56a, 56c, 56e is narrowed. Therefore, the contacts 55a to 55d, 56a, 56c, 56e are wore away by arc discharge occurring at the opening/closing time of the fixed contact 56e and the fixed contact 56a, 56c, that is, at the separate/contact time of the movable contacts 55a to 55d from/to the fixed contacts 56a, 56c, 56e, and generated powder having electrical conductivity adheres to the surface of the insulator between the fixed contacts 56a, 56c, 56e, so that the insulation therebetween may be lost. Furthermore, other foreign matters having electrical conductivity such as water drop or the like may adhere to the surface of the insulator between the fixed contacts 56a, 56c, 56e, so that the insulation therebetween may be lost with high probability. Still furthermore, high precision is required for design, manufacturing and assembling of the contacts 55a to 55d, 56a, 56c, 56e, etc. and respective parts such as the movable piece, the board, etc., and thus the working is difficult. On the other hand, when the contacts 56a to 56d are provided at a position which is farther away from the contact 56e in the right-and-left direction, the insulating interval between the contacts 56a, 56c, 56e is increased, however, the occupational area of the contacts 56a to 56e in the board 56 is enlarged by the amount corresponding to the increase of the insulating interval, so that the power window switch 51 is large in size. Such a problem may likewise occur in the contact structures of the patent documents 1, 2.